Recognized by sight: There are many different Myxogastria with yellow plasmodium and of the 132+ species of Physarum, of which less than half of the plasmodial colors are known, there are 29 known to be yellow.
Many Myxogastria are opportunist and eat whatever is consumable and available around them. They are not host specific. To make an identification from plasmodium alone without fruiting material to examine is truly an assumption anyway.

Recognized by sight: There are many different Myxogastria with yellow plasmodium and of the 132+ species of Physarum, of which less than half of the plasmodial colors are known, there are 29 known to be yellow.
Many Myxogastria are opportunist and eat whatever is consumable and available around them. They are not host specific. To make an identification from plasmodium alone without fruiting material to examine is truly an assumption anyway.